Should I leave or stay?

ok I have been seeing this man for 7yrs,he is 25 I am 28. I have three kids out side our relationship from a past relationship. Two of my kids stay with there father but my boyfriend picks them up from there dad every other weekend and is real good to them My son which is 12yrs old stays with me he helps me raise him Now I have two kids from him 6 month old and a 4 yr old he is a awesome father he works I work etc.He met on a yahoo chatline in 2004 and been together every since I had no signs of him ever wanting to be with another women until.he asked me to call a number he found on craigslist for some dog he was interested in Well I coulden't find the dog he was talking a bout so I went to his his website where he looked and I found some site have been clicked"women seeking men" "men seeking women" Strictly platonic" ..I decided to check out his history on his page and I found a lot more there was about ten pics of girls he was looking at When I confronted him he said I was over reacting That haven't I ever thought about just looking,I caused it on myself...he had and shows no remorse Am I over reacting? Should I leave? What should I do?